With the increasing down-scaling of integrated circuits and the increasingly demanding requirements to the speed of integrated circuits, transistors need to have higher drive currents with increasingly smaller dimensions. Fin Field-Effect Transistors (FinFET) were thus developed. The FinFETs include vertical semiconductor fins above a substrate. The semiconductor fins are used to form source and drain regions, and to form channel regions between the source and drain regions. Shallow Trench Isolation (STI) regions are formed to define the semiconductor fins. The FinFETs also include gate stacks, which are formed on the sidewalls and the top surfaces of the semiconductor fins.
There are various regions that may be formed by implantations. For example, anti-punch-through stoppers may be formed by performing tilted implantations after the etching of a semiconductor substrate to form trenches, which trenches are filled in subsequent steps to form STI regions. The remaining semiconductor strips defined by the trenches have high aspect ratios. Accordingly, the implanted species are unable to reach the bottom portions of the semiconductor strips since the implanted species are blocked by neighboring semiconductor strips.